Measurements of hot targets such as red or white hot ingots or slabs in a steel mill have always been difficult and in the case of ultrasonic measurements, the problem has been compounded by the fact that the hot slab is typically radiating tremendous heat creating a large number of temperature gradients in the air between the transducer and the target. Positioning one or more temperature sensors or other means utilized to determine the speed of sound in a given medium does not result in a good practical solution to the problem because of the wide differential in temperature in the measuring path air between the hot slab and the location at the ultrasonic transducer. Moreover, extreme temperatures of the hot target causes turbulent air flow around the target and this turbulent air flow also can cause variations in the time of travel of the ultrasonic energy to and from the hot ingot target.
I have discovered that by blowing air in the path between the transducer and the hot target, sharp temperature gradients are reduced and adverse effects of the temperature gradients on range measurement accuracy is greatly diminished or minimized. Moreover, the hot turbulent air flow in the measuring path is displaced to permit accurate measurement.
The object of this invention is to provide an improved ultrasonic measurement of hot targets by the elimination of temperature gradients and hot turbulent air flow into the measuring path between the ultrasonic transducer and the hot target such as a steel ingot. In a preferred embodiment, a fluid medium such as air under pressure is flowed from the transducer to the target to form a homogeneous column of air flowing towards and impinging upon the hot target to thereby establish an ultrasonic measuring path between the target and the ultrasonic transducer. This establishes an "artificial" measuring path between the ultrasonic transducer and the hot slab target in which the air is of substantially constant temperature and turbulent hot air flows at least in the measuring path area of the target is eliminated or minimized. Radiant heat from the target heats a thin layer of air but the high pressure jet of air from the target forms a measuring path column of air that is substantially homogeneous with respect to temperature and hence with respect to speed of ultrasonic energy in the medium. The air is caused to issue from a manifold which has one jet exiting into a plenum chamber containing the a temperature sensor and a plurality of jets circumferentially spaced around the transducer so as to provide as uniform and as turbulent-free a measuring path without the entrainment of too much ambient air into the measuring path.
Since the hot target may be radiating a large amount of thermal energy, the transducer itself is not in a direct line to the hot target but, rather, is positioned above a 45 degree reflector which has been painted with a black or an absorbent paint which prevents reflection of the radiant energy into the transducer. In a preferred embodiment, the transducer is a planar electrostatic transducer of the type sold by the Polaroid.TM. company but, in other embodiments can use more expensive transducers such as piezoelectric crystals including barium titanate and the like. The air flows into the plenum chamber is relatively cool and serves to cool the ultrasonic transducer, reflector and electronic circuitry therein.
Thus, the invention has the object of solving the problem of measuring any hot surface such as a red-hot slab such as a steel ingot in a mill. The column of air establishes a uniform homogeneous measuring path to within a very short distance of the target where the extreme heat of the target has significantly less effect on the measurement and can be better calibrated for accuracy. The transducer itself is contained within a plenum chamber and projects an narrow ultrasonic beam upon the 45 degree reflector so that the beam exists through an aperture or opening into a cowled chamber and the plurality of jet nozzles issue jets of high pressure air which merge into a homogenous column of air. For long range measurements (15-60 inches) at lower frequency, the jets are located outside the cowl and the cowl serves as a noise shield. For short range measurements at a higher frequency, the jet nozzles are located inside the cowled chamber and circumferentially spaced around the exit aperture adjacent the 45 degree reflector. The cowling itself may be a stainless-steel cylinder around or through which the column of air flows towards target and the target in space from 5 to about 45 inches from the end of the cowling. Separate regulator valve may be incorporated for adjusting the air flow interior of the plenum chamber and adjusting the air flowing through the circumferentially spaced jet nozzles. The housing may be insulated to protect the interior from heating excessively and creating temperature differentials in the portion of the measuring path MP which is located in the plenum chamber and hence temperature gradients which can adversely effect the measurement.